"DIY" reverse GND?

I had an idea about reverse GNDs the other morning. not really making my own, but using what I have to make it work and have the second transition be adjustable....

so, take your standard GND filter:

****
****
****
****
****
****

now, take a 1 stop GND, and flip it upside down:
****
****
****
****
****
****

now consider that you only use ~4 lines of the 6 I've shown in these "diagrams" right? At least with a 4x6 filter I can shove it ALL the way into my holder and use it as an ND covering the entire frame, so bear with me with that assumption...

so, set the 2 filters up like this (showing only 4 lines)
let's assume you're using a 3 stop GND on the left and 1 stop GND on the right:

**** | **** 3 stops, net 2
**** | **** 4 stops, net 3
**** | **** 1 stop, net 0
**** | **** 1 stop, net 0


that would basically work like a 2 stop GND reverse, no? Because you have at least one stop of ND at every point in the image, you reduce the strength across the whole image making the net strengths the correct relative strengths right, but effectively the whole scene is reduced in light 1 additional stop beyond using the same reverse GND? Would this work? I'm just having a hard time justifying a singray reverse, and my hitech reverse isn't cutting it for me (the length of the middle section is so long it's basically a normal GND, because of this I've been thinking an adjustable GND like this would work better than a set distance anyway).

I'm not getting how this would work like a reverse GND. Or at least, not like the ones I've seen used for sunrises and sunsets.

AFAIK, the reverse GND is darker in the middle to hold back the area along the horizon but your arrangement would still be darker top and bottom than in the middle.

here's what my reverse looks like:
**** 2 stops
**** 3 stops
**** 3 stops
**** clear
**** clear
**** clear

check the math/last diagram I posted in the OP. While there is SOME tint/ND at all places in the image, effectively you're getting the same thing no? You control the thickness of the darkest part by sliding the 1 stop down and you set the 3 stop where you'd use it anyway?

this is what it'd look like using 2 filters:
**** 2 stops net (clear from the reversed filter, 3 from the 3 stop GND, reduced 1 stop because the whole thing has at least 1 stop covering the lens)
**** 3 stops net, 1 from the 1 stop GND, 3 from the 3 stop GND, reduced 1 for whole frame having 1 stop reduction)
**** 0 stop net, 1 stop from 1 stop GND but the entire frame has at least this much ND
**** 0 stop net, 1 stop from 1 stop GND but the entire frame has at least this much ND

basically the same end result right?

Looks like it might work, Ben. However, you'd need at least the stronger one to be a hard grad. Not sure whether you'd want a hard or soft 1-stop for best results. I'm thinking maybe a soft. Tell you what - run a few tests for us :{)#

Personally, I think I'd rather get a real reverse grad than have to haul around a 1-stop grad of the appropriate transition, that I would be unlikely to use for anything else anyhow.

I have to agree with Jon. How often would you really use this combo?

I agree on the hard transition but I use bards anyway @ 17mm on FF. As for why this over a dedicated reverse, my issue is the HiTech I just bought isn't usable and the sings are too rich for my blood. I'm going to play with what I have this am for proof of concept (I'm on my iPhone in a parking lot right now) and see.

FlyingPhotog wrote in post #12093669
I'm not getting how this would work like a reverse GND. Or at least, not like the ones I've seen used for sunrises and sunsets.

AFAIK, the reverse GND is darker in the middle to hold back the area along the horizon but your arrangement would still be darker top and bottom than in the middle.

I gotta agree. Seems like too much to fiddle with to get "just right", with probably a lot of extra PP time to mask certain areas that may be underexposed.

OP: Why isn't the Hitech reverse working for you? I've seen plenty of shots taken with the filter in various fora and they look pretty good. IIRC, Kevindar (member here) uses one and I haven't seen any complaints from him.

argyle wrote in post #12095787
OP: Why isn't the Hitech reverse working for you?

I think mine is made wrong (they won't reply to emails :mad. The second transition is so far from the normal grad transition that with my 17-40 @ 17mm on FF I need to compose a vertical shot with the horizon more then 3/4 of the way DOWN into the frame to even see the effect. I can't even get it into the frame if I shoot horizontally or zoom in at all... So I either got a dud, or they're not designed for 17mm on FF.

Using 2 filters like I'm explaining allows me to custom fit the reverse section into the frame EXACTLY where needed. And after some testing this morning it seems to work pretty well. Granted I don't have the exact parts I want, but with my Lee 2.5 hard filter (my only lee filter right now) and a friends cokin 1 stop soft GND, it worked perfectly. I'll have sample shots up later. My hitech reverse did it's typical no second transition BS in the same scene with the horizon about in the middle of the frame....

So while you have to deal with 2 filters (so 4 surfaces) it DOES work better if you can deal with the layers of glass. I also use a Lee CP, so that's another 2 layers...... The other issue is because you lose a stop of GND effectively, you're stuck with only being able to use this with 2 effective stops of GND control in a scene assuming Lee only makes a 3 stop hard (and 1.5 stops using the 2.5 GND I already have). But I'm thinking that's not a huge loss because the scenes when I want a reverse, it seems like the sun isn't so bright I need a 3 stop? We'll see.

But I'll be ordering a 1 stop soft and 3 stop hard Lee as soon as I can get the funding for it. For me, it makes more sense than a reverse I think. At least after my experience with a formatt/hitech reverse that doesn't make it into the scene unless I'm VERY specific in composing for it (17mm vertical on FF with the horizon intentionally low).

You're theory is correct. How usable or convenient it is, I don't know. I used to mess around in LR3 to try and simulate the reverse GND effect by doing exactly what you described, but digitally. I'd have to increase total image exposure to +1 to get the effect. And doing it digitally, if an area is blown out on capture, nothing you can do. But I can at least verify your calculations and theory are correct.

I stopped agonizing over it and shelled out the money for the SR reverse...

Haven't used it yet because of the torrential downpour...

projectmayhem713 wrote in post #12096972
You're theory is correct. How usable or convenient it is, I don't know. I used to mess around in LR3 to try and simulate the reverse GND effect by doing exactly what you described, but digitally. I'd have to increase total image exposure to +1 to get the effect. And doing it digitally, if an area is blown out on capture, nothing you can do. But I can at least verify your calculations and theory are correct.

that's exactly my problem...

I like to get things right in camera in one exposure. I don't need a reverse all that often, but when I do, having a set second transition doesn't seem to work for me, at least not the hitech I have. I don't like HDR or exposure blends because I shoot around water so often it's tricky to get 2 shots that line up right, and I'm constantly taking multiple shots of the same scene just to time a wave right, once you start using multiple shots exposure wise that becomes a nightmare.

jacobsen1 wrote in post #12097051
that's exactly my problem...

I like to get things right in camera in one exposure. I don't need a reverse all that often, but when I do, having a set second transition doesn't seem to work for me, at least not the hitech I have. I don't like HDR or exposure blends because I shoot around water so often it's tricky to get 2 shots that line up right, and I'm constantly taking multiple shots of the same scene just to time a wave right, once you start using multiple shots exposure wise that becomes a nightmare.

You've definitely convinced me that you should get a Singh ray. You could offset the cost by selling the hitech?

It makes sense to me. It's like an adjustable reverse GND filter. I've never used filters, but I assume these were made with the intention to shoot as wide as possible. If you changed your composition (moving or zooming), I'm guessing the S-R (or whichever company) filter may not be in the optimum position.

Let's say you were at a bay shooting the sunset. You're done shooting a wide shot of the sun setting over the ocean and see a bluff off to the side. I'm guessing that if you zoomed in, the preset distance of the gradation might not be as optimal. Am i correct in this assumption? So using two filters with the ability to adjust it would be better (assuming you had the time to set it all up).

Just buy a Singh Ray Ben. An alternative as you described is inconvenient imho. I seriously don't have issues with my SR grad.

If I understand you correctly, there will be 3 zones of varying ND rating: a zone (lowest or highest, depending on which GND has clear area at top vs bottom) that will have an ND of the lower GND, an overlap zone equal to the aggregate of the 2 GND used (ie +1 & +3 = +4 in your example), and a 3rd zone equal to the "other" GNDs rating. You could use any 2 GNDs (ie 1+1= 1, 2, 1 GND; 1+2=1,3,2; 2+2=2,4,2; 1+3=1,4,3; etc).

A downside is that rather just lessen the brighter part of the scene you are lessening ALL of the scene by minimally at least the lower GND's ND rating.....a luxury that may not always be practical, ie shutter speed and breezy conditions or moving elements.

The upside is that YOU get to control the width (ie height of transition zone) of the darkest area by virtue of the amount of overlap AND the positioning of that band within the image's frame. You also have the option (assuming you have the right GNDs) to create either 3 zones (ie 2 different ND rated GNDs) or just 2 zones (ie 2 same rated GNDs).

HOWEVER, the issue might be the amount of overlap play and positioning variability before you risk getting one or the other GND's edges into the FOV. Assume the transition is at midheight (I tested mine and they're NOT quite), ie 55-60mm. Using a P size GND as an example, ie 110-120mm long by 85mm wide, the 2 GND (one reversed) would minimally overlap (ie aggregate ND) if overlaid exactly. As you slid one past the other you'd start to get an aggregate ND rating that would exceed the rating of the greater GND's rating (the "harder" the edge, the faster this would occur). At some point the aggregate zone's width (ie > 25mm) edges start to risk being seen (again, depending on FOV of lens and size/length of GND used), AND that assumes that you want the aggregate effect positioned mid height....not likely. If your "width" requirement is fairly narrow then this should be very feasible.

While I haven't used GNDs this way I have used 2 stacked, one reversed with the greater used to mute the sky at top of the scene and the reversed lesser one to mute the sky's reflection at the bottom of the scene, allowing detail in the mountains/forested shoreline.

projectmayhem713 wrote in post #12097517
You could offset the cost by selling the hitech?

yeah, I'll be selling my hitech reverse and 10-stop if I can find a buyer for either pretty soon here.

jdizzle wrote in post #12098320
Just buy a Singh Ray Ben. An alternative as you described is inconvenient imho. I seriously don't have issues with my SR grad.

my issue is I'm not sold on a set second transition... Having seen how it simply doesn't work with my hitech, while I think the singh will be better made, it still can't work in ANY scene in terms of placing both transitions? Yes 2 filters (really three when you factor in my CP) is a massive PITA, even in just a cleaning aspect, but the fact it can be exact is very appealing. Plus, it means I'm carrying more Lee GNDs which I prefer anyway? The 1 stop could be used for other scenes as well. When I had my cokin Xs I had a 1 2 and 3 and I actually used the 1 more than I thought I would (sometimes stacked with a 3, sometimes alone, this would give it a third use).

Russ61 wrote in post #12098596
If I understand you correctly, there will be 3 zones of varying ND rating

correct

correct again. The biggest issue I see is when I run out of GND, IE with a 3 stop in the top and a 1 in the bottom the 3 stop is only bringing the sky down 2 relative stops, which could be not enough. As for the timing of all these stops, not an issue, I rarely if ever have too slow a shutter speed, but often too fast, even with NDs and CPs.

exactly

nope, not with 4x6 GNDs on my lee system on my 17-40mm on FF. I can actually use a normal GND as a ND with my setup, there's enough room, so I'd never have issues with the edges in shots unless I make a mistake.